The invention is generally related to valves for throttling the flow of combustion air to an internal combustion engine. More particularly, the invention is related to such valves made from plastic.
Throttle valves for large automotive and industrial internal combustion engines have traditionally been made from light metal alloys such as magnesium and aluminum. These materials are resistant to the elevated temperatures in the engine compartments of modern vehicles. They can also be molded to the tight dimensional tolerances required for accurate and repeatable control of air flow over long lifespans of these engines. They also have the strength and stiffness required to support large diameter butterfly valves (typically 50-85 mm) needed for the large volumetric flow rates of such engines.
Automotive throttle valves typically are typically butterfly valves. Butterfly valves have a roughly circular plate called butterfly that is disposed in the circular throat of a throttle body to pass or to block flow, depending upon its rotational position. The butterfly is typically fixed to a throttle shaft that extends across the throat of the throttle body generally perpendicular to the direction if combustion air flow. The throttle shaft extends through at least one the wall of throttle body and is connected to a throttle lever disposed on the outside of the throttle body to rotate the shaft and thereby open and close the throttle valve.
Recently, throttle valves have been proposed and made using a variety of plastic components. For example, the Rover K-3 employs a plastic throttle body with a metal shaft and a plastic bearing insert. U.S. Pat. No. 5,769,045 discloses a plastic throttle body with steel shaft and a metal needle roller bearing insert in the throttle body. U.S. Pat. No. 5,304,336 shows a throttle valve having a plastic throttle body and a simultaneously molded throttle body, shaft, and butterfly. U.S. Pat. No. 5,666,988 discloses a plastic throttle shaft. U.S. Pat. No. 5,098,064 discloses a plastic throttle body with metal bearing inserts for supporting a metal throttle shaft. An example is shown in FIGS. 4A-B. All of these constructions have problems.
There are several problems faced by a manufacturer of throttle valves with plastic components. Among others, throttle body wear is significant. To reduce wear, bearings or bushings are typically into a plastic throttle body to support the throttle valve shaft. High temperatures in engine compartments also pose problems. Creep at elevated temperatures may cause a plastic throttle shaft and butterfly to deform, requiring frequent vehicle tune-ups. If both the throttle body and the throttle shaft are made of plastic, the problems with wear and creep are enhanced since both parts may creep and wear, increasing the probability of misalignment, leakage and failure.
The very manufacture of throttle valves having plastic throttle bodies and plastic shafts is fraught with difficulties. Unless plastic components are carefully designed and made with critical attention paid to wall thicknesses, material selection, cooling rates, and plastic injection pressure to mention but a few factors, they are prone to shrink and deform, which causes misalignment, leakage around the shaft or the butterfly, and even accelerated wear.
The patents cited above suggest several solutions to some of the problems presented by the use of plastics. Unfortunately, the solutions themselves generate their own problems. For example, plastic or metal bearings or bushing may be inserted into bosses extending from the throttle body to support the throttle shaft. This, however, requires large diameter plastic bosses extending from the surface of the throttle body into which the bearing or bushing can be inserted to support the throttle shaft and reduce wear. Unfortunately, these large bosses cause distortion of the throttle body throat, and prevent the throttle valve butterfly from fitting properly into the throat of the throttle body. This distortion is due largely to the increased volumetric ratio of the bosses in relation to the throat itself. The large bosses draw a substantial amount of plastic away from the primary task of filling out the throat of the throttle body. This delays packing out the throat of the throttle body (with pressure) and results in distortion of the throttle body throat, as well as sinks at the bosses themselves. These distortions and sinks prevent a (separately molded) butterfly from properly sealing the throat closed when the butterfly is later inserted into the throat and attached to the throttle shaft. At the very least, these problems require significant throttle body mold alterations and tuning, as well as a precise control of the molding process itself to insure a proper fit between the butterfly and throat.
Another method of avoiding the distortion, sealing and wear problems is to simultaneously mold both the throttle body and the throttle shaft, as shown in U.S. Pat. No. 5,304,336. In this process, the throttle shaft and throttle body are molded in a single manufacturing process, first the throttle body, and then the throttle shaft and integral butterfly. Once the body is molded, the pins that form the interior of the throat and those that form the holes in the bosses that support the throttle shaft are partially withdrawn and molten plastic is injected into the void that is thereby created. In this manner, the just-molded hollow bosses and the interior walls of the throttle body become part of the xe2x80x9cmoldxe2x80x9d and themselves form the throttle shaft and integral butterfly. Distortion and warping are less of a problem in this process, since the throttle shaft and butterfly are formed by the just-molded throttle body itself, rather than being separately molded and later inserted into the throttle body.
While this last process improves sealing by, in effect, custom mating each plastic throttle shaft and butterfly to the plastic throttle body, it requires the use of two quite different thermoplastics: a higher melting point plastic to form the throttle body, and a significantly lower melting point plastic to form the shaft and butterfly. It has also required that manufacturers mold the throttle body using a structural plastic mixed with PTFE (polytetrafluoroethylene). The PTFE acts as a mold release agent and insures that the molded-in-place shaft and butterfly do not stick to the throttle body when it is formed. Unfortunately, it also requires complex molding equipment and precise timing and sequencing of the two-stage injection molding process.
What is needed, therefore is an improved throttle valve construction that may employ a smaller boss to minimize throat distortion, yet does not require complex multistage molding operations, and provides an accurately dimensioned throat that seals satisfactorily to a subsequently inserted and separately molded butterfly.
It is an object of this invention to provide such a throttle valve.
In accordance with the present invention, an improved throttle valve for controlling the flow of combustion air to an internal combustion engine is provided having a throttle body, and a throttle shaft made of a plastic filled with solid lubricant, and a butterfly attached to the throttle shaft.
In accordance with another embodiment of the invention, a throttle valve for throttling the flow of combustion air to an internal combustion engine is provided including, a plastic throttle body that has a throat for passing combustion air and an intersecting passageway that supports the throttle shaft, a plastic throttle shaft filled with a solid lubricant that extends through the intersecting passageway, and a butterfly attached to the shaft for rotation in the throat to throttle the flow of combustion air. The passageway is generally perpendicular to the throat and is defined by two bosses that are molded integral with the throttle body and have an inner molded surface that contacts and supports the throttle shaft. The throttle shaft is integrally molded with a throttle arm that engages a throttle shaft rotating means. The throttle shaft may include at least one boss to which the butterfly is fixed.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.